This lab proposes to systematically, genetically dissect the 5S rRNA locus in Drosophila melanogaster. The molecular organization of the entire cluster and isolated mutants will be analyzed by 1) saturation hybridization, 2) restriction endonuclease mapping and 3) cloning of flanking 5SrDNA sequences and interband 5SrDNA. The effect of these mutants upon chromosome structure can be determined by cytology of polytene chromosomes and by molecular means, whether the mutants have interband DNA. The genes that connrol the replication of 5SrDNA and Y chromosome 18 and 28SrDNA will be genetically analyzed. The phenomena of position-effect variegation upon redundant loci will also be examined.